The first point that needs to be made is that oral traditions are frequently very accurate. They are passed on with exceptional care. As far as the New Testament is concerned
1) Pauls Epistles were written first. I saw a presbytarian expert on television who claimed that only three were genuine. The rest were written by other people. As far as the gospels are concerned they are suspected to have been based on a older text now lost.
2) Remember that the Christians had a conference in Ephesus (Site of one of the ancient wonders of the world) to decide what to include in the New Teatament. This issue still is devisive
The catholic bible includes the apochrypha. The prostestant and orthodox bibles do not. I also believe that the Orthodox Bible does not include the Book Of Revelations. I do not know what the coptic bible includes.
A strong case can be made for including "The Gospel of Saint Thomas" which was found some years ago in Egypt
